In the process of broadband and mobilization development of a network, the 3rd Generation Partnership Program (3GPP) organization proposes a Long Term Evolution (LTE) solution, that is, Evolved Universal Mobile Telecommunication System (UMTS) Territorial Radio Access Network (E-UTRAN) in a mobile access network and a System Architecture Evolution (SAE) solution, that is, Evolved Packet Core (EPC), in a mobile core network.
The E-UTRAN adopts a single layer structure including only an evolved base station (Node B, eNB), so as to simplify the network and reduce network delay. The structure actually approaches a typical Internet Protocol (IP) broadband network structure. A traditional cellular network is a star topology network centering on a base station and adopts centralized control, so a User Equipment (UE) directly access the network through the eNB in the current LTE protocol.